Pneumatic tires commonly comprise air tight tubes for confining fluid, such as air, within the tire. The tire tube is provided with a valve stem for introduction of air into the tube. The valve stem includes an inner core generally comprising a one way check valve.
Loss of air from an pneumatic tire's tube may occur through either a puncture in the tube, or a malfunction of the check valve in the valve stem core. Repair of a punctured tube typically requires removal of the tube from the wheel rim carrying the tire. Repair of a malfunctioning valve stem core, on the other hand, can usually be accomplished without removal of the tire tube from the rim of the wheel. Accordingly, a device which indicated leakage of air through a valve core stem would greatly facilitate the repair of pneumatic tires, by indicating whether or not the failure of the tire was due to a punctured tube or a malfunctioning valve stem core.